Methods and breakable supports for additive manufacturing

ABSTRACT

The present disclosure generally relates to methods for additive manufacturing (AM) that utilize breakable structures in the process of building objects, as well as novel breakable support structures to be used within these AM processes. A support structure includes a weakened portion and the object includes an outlet. The method includes breaking the removable support structure at the weakened portion into at least two parts.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and is a continuation applicationof, U.S. patent application Ser. No. 15/042,001 filed Feb. 11, 2016,titled “Methods and Breakable Supports for Additive Manufacturing,”which is hereby expressly incorporated herein by reference in theirentirety.

INTRODUCTION

The present disclosure generally relates to methods for additivemanufacturing (AM) that utilize support structures in the process ofbuilding objects, as well as novel support structures to be used withinthese AM processes.

BACKGROUND

AM processes generally involve the buildup of one or more materials tomake a net or near net shape (NNS) object, in contrast to subtractivemanufacturing methods. Though “additive manufacturing” is an industrystandard term (ASTM F2792), AM encompasses various manufacturing andprototyping techniques known under a variety of names, includingfreeform fabrication, 3D printing, rapid prototyping/tooling, etc. AMtechniques are capable of fabricating complex components from a widevariety of materials. Generally, a freestanding object can be fabricatedfrom a computer aided design (CAD) model. A particular type of AMprocess uses an energy beam, for example, an electron beam orelectromagnetic radiation such as a laser beam, to sinter or melt apowder material, creating a solid three-dimensional object in whichparticles of the powder material are bonded together. Different materialsystems, for example, engineering plastics, thermoplastic elastomers,metals, and ceramics are in use. Laser sintering or melting is a notableAM process for rapid fabrication of functional prototypes and tools.Applications include direct manufacturing of complex workpieces,patterns for investment casting, metal molds for injection molding anddie casting, and molds and cores for sand casting. Fabrication ofprototype objects to enhance communication and testing of conceptsduring the design cycle are other common usages of AM processes.

Selective laser sintering, direct laser sintering, selective lasermelting, and direct laser melting are common industry terms used torefer to producing three-dimensional (3D) objects by using a laser beamto sinter or melt a fine powder. For example, U.S. Pat. Nos. 4,863,538and 5,460,758 describe conventional laser sintering techniques. Moreaccurately, sintering entails fusing (agglomerating) particles of apowder at a temperature below the melting point of the powder material,whereas melting entails fully melting particles of a powder to form asolid homogeneous mass. The physical processes associated with lasersintering or laser melting include heat transfer to a powder materialand then either sintering or melting the powder material. Although thelaser sintering and melting processes can be applied to a broad range ofpowder materials, the scientific and technical aspects of the productionroute, for example, sintering or melting rate and the effects ofprocessing parameters on the microstructural evolution during the layermanufacturing process have not been well understood. This method offabrication is accompanied by multiple modes of heat, mass and momentumtransfer, and chemical reactions that make the process very complex.

FIG. 1 is schematic diagram showing a cross-sectional view of anexemplary conventional system 100 for direct metal laser sintering(DMLS) or direct metal laser melting (DMLM). The apparatus 100 buildsobjects, for example, the part 122, in a layer-by-layer manner bysintering or melting a powder material (not shown) using an energy beam136 generated by a source such as a laser 120. The powder to be meltedby the energy beam is supplied by reservoir 126 and spread evenly over abuild plate 114 using a recoater arm 116 travelling in direction 134 tomaintain the powder at a level 118 and remove excess powder materialextending above the powder level 118 to waste container 128. The energybeam 136 sinters or melts a cross sectional layer of the object beingbuilt under control of the galvo scanner 132. The build plate 114 islowered and another layer of powder is spread over the build plate andobject being built, followed by successive melting/sintering of thepowder by the laser 120. The process is repeated until the part 122 iscompletely built up from the melted/sintered powder material. The laser120 may be controlled by a computer system including a processor and amemory. The computer system may determine a scan pattern for each layerand control laser 120 to irradiate the powder material according to thescan pattern. After fabrication of the part 122 is complete, variouspost-processing procedures may be applied to the part 122. Postprocessing procedures include removal of access powder by, for example,blowing or vacuuming. Other post processing procedures include a stressrelease process. Additionally, thermal and chemical post processingprocedures can be used to finish the part 122.

During laser sintering/melting processes, the three-dimensional objectis subject to numerous stresses due to the recoating of additionallayers of powder as the object is built. The present inventors havediscovered that certain AM structures, for example hollow structures,tend to experience deformation. In some cases, the deformation mayrelate to the movement of the recoater arm as it moves past the objectbeing built. In view of the above, it can be appreciated that there areproblems, shortcomings or disadvantages associated with AM techniques,and that it would be desirable if improved methods of supporting objectsand support structures were available.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its purpose is to presentsome concepts of one or more aspects in a simplified form as a preludeto the more detailed description that is presented later.

In one aspect, the disclosure provides a method for fabricating anobject in a powder bed, comprising the steps of: (a) irradiating a layerof powder in the powder bed to form a fused region; (b) providing asubsequent layer of powder over the powder bed by passing a recoater armover the powder bed from a first side of the powder bed; and (c)repeating steps (a) and (b) until the object and at least one supportstructure is formed in the powder bed, wherein the support structurecomprises a weakened portion and the object comprises an outlet; and (d)breaking the removable support structure at the weakened portion into atleast two parts.

These and other aspects of the invention will become more fullyunderstood upon a review of the detailed description, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic diagram showing an example of a conventionalapparatus for additive manufacturing.

FIG. 2 illustrates a perspective view of an example of an objectsupported by a support structure in accordance with aspects of thepresent invention.

FIG. 3 illustrates a perspective view of the example object and supportstructure of FIG. 2 with the object transparent, in accordance withaspects of the present invention.

FIG. 4 illustrates a front view the example support structure of FIG. 2in accordance with aspects of the present invention.

FIG. 5 illustrates a front view of the example support structure of FIG.2 after breaking the support structure in accordance with aspects of thepresent invention.

FIG. 6 illustrates a perspective view of a portion of the examplesupport structure of FIG. 2 after breaking and being partially removedfrom the example object of FIG. 2 in accordance with aspects of thepresent invention.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails.

FIGS. 2 and 3 illustrate an example object 200 surrounding an examplesupport structure 210. FIG. 3 shows the object 200 transparently so thatthe support structure 210 within the object 200 is visible. FIG. 4 showsa front view of the support structure 210 with the object 200 omittedfor clarity. The support structure 210 and the object 200 may bemanufactured according to an AM process. For example, the apparatus 100of FIG. 1 and method described above may be used. In this type of AMprocess, the object 200 is built layer-by-layer by selectively sinteringor melting areas of the powder in the regions that form the object 200.The support structure 210 is built simultaneously with the object 200 bymelting or sintering additional regions of the powder in the location ofthe support structure 210. The arrows 205 in FIGS. 2 and 3 denote thedirection of the recoater arm as it provides a fresh layer of powder ateach stage of the object's build. Preferably, the support structure 210is within the object 200 along the direction of the recoater arm.

Upon completion of the AM process, the support structure 210 is removedfrom the object 200. In one aspect, the support structure 210 isattached along with the object to the build plate and may be detachedfrom the build plate and discarded. The support structure 210 mayalternatively be formed without attachment to the build plate as a freestanding object within the powder bed. In addition, the supportstructure may include a point of attachment to the object 200 that maybe readily broken away once the AM process is complete. This may beaccomplished by providing a breakaway structure—a small tab of metaljoining the object 200 and support structure 210. The breakawaystructure may also resemble a perforation with several portions of metaljoining the object 200 and support structure 210.

The removal of the support structure 210 from the object 200 may takeplace immediately upon, or during, removal of the object from the powderbed. Alternatively, the support structure may be removed after any oneof the post-treatment steps. For example, the object 200 and supportstructure 210 may be subjected to a post-anneal treatment and/orchemical treatment and then subsequently removed from the object 200and/or build plate. As will be discussed in more detail below, thesupport structure 210 may be broken into a plurality of pieces (e.g., 2or more) as part of the removal process.

The present inventors have found that support structures 210 areparticularly desirable in forming objects 200 that have hollow internalspaces, such as spherical shapes. In the example aspect illustrated inFIGS. 2 to 6, the object 200 may include a wider first portion 202 thattransitions into a narrower second portion 204. For example, asillustrated in FIG. 2, the wider first portion 202 may be a sphericalshaped portion having a first diameter and narrower second portion 204may be a cylindrical portion having a second diameter, where the firstdiameter is larger than the second diameter. Each of the first andsecond portions 202, 204 of the object 200 may be hollow (FIG. 3).Because the object 200 may be hollow, the support structure 210 may beused internally along the recoater direction to support the object 200as part of the object manufacturing process. The object 210 may furtherinclude an outlet 206. The outlet 206 may be located at the end of thesecond portion 204 of the object 200.

As illustrated in FIG. 3, the support structure 210 may have a congruentgeometry to match the inside shape of the object 200. For example, thesupport structure 210 may include a first portion 212 that fits withinand contacts the inside surface of the first portion 202 of the object200 and may include a second portion 214 that fits within and contactsthe inside surface of the portion 204 of the object 200. As illustratedin FIG. 3, the first portion 212 and the second portion 214 of thesupport structure 210 need not cover the entire inside surface of thefirst and second portions 202, 204 of the object 200. For example, thefirst portion 212 of the support structure 210 may have a circular diskshape rather than a sphere shape. The first portion 212 may have a widththat is approximately equal to the diameter of the first portion 202 ofthe object 200. However, the thickness of the first portion 212 may bemany times smaller than the diameter of the first portion 202 of theobject 200. For example, the ratio of the diameter of the first portion202 of the object 200 to the thickness of the first portion 212 of thesupport structure 210 may be 50:1 to 5:1, 40:1 to 10:1, or 30:1 to 20:1.Any dimensions of the first portion 212 of the support structure 210that are sufficient to internally support the hollow first portion 202of the object 200 may be used. With respect to the second portion 214 ofthe support structure 210, it may have thin rectangular shape ratherthan a cylindrical shape. The rectangular shape may have a width that isapproximately equal to the diameter of the second portion 204 of theobject 200. However, the thickness of the second portion 214 of thesupport structure 210 may be many times smaller than the diameter of thesecond portion 204 of the object 200. For example, the ratio of thediameter of the first portion 202 of the object 200 to the thickness ofthe second portion 214 of the support structure 210 may be 50:1 to 5:1,40:1 to 10:1, or 30:1 to 20:1. Any dimensions of the second portion 214of the support structure 210 that are sufficient to internally supportthe hollow second portion 204 of the object 200 may be used. The same isapplicable to the second portion 214 of the support structure 210.

The support structure 210 may further include a weakened portion 216. Asillustrated in FIGS. 3 and 4, the weakened portion may include a notch220 and a perforation 218. The notch 220 may be disposed at a peripheryof the second portion 214 of the support structure 210. The term notchis meant to include any interruption in the border of the structure thatserves as a starting point for breaking and/or tearing. Thus, the termnotch includes, nick, slit, slot, split, slash, cut, divide, and thelike. The notch may be triangular in shape. As shown in FIG. 4, thetriangular notch may be oriented such that a point of the notch pointsdirectly towards the second portion 214 of the support structure 210. Atriangular notch having such an orientation allows the operator toeasily start a break/tear line at the apex of the triangle notch. It iswithin the scope of the invention, however, that any shaped notch orequivalent thereof can be used. For example, the notch may be a slit orany other shape capable of introducing a break/tear line into thesupport structure 210. Generally, the notch is large enough to allow theoperator to begin a break/tear line by applying a breaking/tearing forceat the notch. The perforation 218 may begin from the apex of the notch220 and extend all the way along the entire height/length of the supportstructure 210, terminating at the end of the first portion 212 of thesupport structure 210. The perforation 218 may include perforated lines,score lines, partial-score lines, non-continuous cut lines, or any otherseries of holes, deformations, dimples, depressions, or points ofreduced thickness for facilitating a break/tear line through the supportstructure 210.

As illustrated in FIG. 3, due to the geometry of the support structure210 and geometry of the object 200, and more particularly due to thegeometry of the first portion 212 of the support structure 210 have awidth greater than the diameter of the second portion 204 of the object200, the support structure 210, it is not possible to remove the entiresupport structure 210 directly downwardly through the opening 206. Forexample, if one were to attempt to pull support structure 210 downwardlythrough the outlet 206 without breaking/tearing it, first portion 212 ofthe support structure 210 would prevent the movement. However, bybreaking the support structure 210 via the weakened portion 216 into twosmaller pieces (FIG. 5), the operator can then remove one piece at atime through the outlet 206. FIG. 5 shows the support structure 210split along the perforation 218. FIG. 6 shows one half of the supportstructure 210 being removed through the outlet 206 after breaking thesupport structure 210.

While FIGS. 2-6 show example geometries in which a support structure maypass through an outlet of the object after breaking the supportstructure, any variety of geometries for the support structure and theobject may be selected. Generally, the support structure and the objectwill have congruent geometries. Furthermore, while FIGS. 2-6 show asingle notch and a single perforated line for breaking the supportstructure into two pieces, any number of notches (e.g., 2, 3, 4, 5,etc.) and corresponding perforations may be implemented to break thesupport structure into multiple pieces. The support structure 210provides mechanical support to the object to prevent distortion due tostress or recoater contact.

While not illustrated, the support structure 210 may further include onemore connecting rib integrally connected with the object 200. Theconnecting ribs would extend from the surface of the support structureto the inner surface of the object 200. The connecting ribs may beformed incrementally along the height of the support structure 210. Theconnecting rib may form a breakaway structure that allows removal of thesupport structure 210 from the object 200 as desired.

When it becomes necessary to remove the support structure 210 from theobject 200 the operator may apply force to break the support structurefree when connecting ribs are present. The support structure may beremoved by mechanical procedures such as twisting, breaking, cutting,grinding, filing, or polishing. Additionally, thermal and chemical postprocessing procedures may be used to finish the object. When powder hasbeen placed between the object and the support structure duringmanufacturing, the powder can simply be removed by blowing, for example.The operator may then further apply a tearing or breaking force via thenotch 220 to impart a breaking or tearing along the perforation 218. Theapplication of force may be applied to cause the support structure 210to tear/break all the way along the perforation 218 (FIG. 5). Oncebroken into pieces, the operator may then remove one piece at a timethrough the outlet 206 of the object 200 (FIG. 6).

Although several examples of support structures and objects have beenprovided, it should be apparent that other objects may be built inaccordance with the present disclosure. For example, any object havinghigh aspect ratio and think walls may be supported by one or more of thedisclosed support structures. In an aspect, the disclosed supportstructures are used to manufacture parts for aircraft. For example, afuel nozzle similar to the one disclosed in U.S. Pat. No. 9,188,341 maybe manufactured using support structures disclosed herein.

In an aspect, multiple supports described above may be used incombination to support fabrication of an object, prevent movement of theobject, and/or control thermal properties of the object. That is,fabricating an object using additive manufacturing may include use ofone or more of: scaffolding, tie-down supports, break-away supports,lateral supports, conformal supports, connecting supports, surroundingsupports, keyway supports, breakable supports, leading edge supports, orpowder removal ports. The following patent applications includedisclosure of these supports and methods of their use:

U.S. patent application Ser. No. 15/042,019, titled “METHOD ANDCONFORMAL SUPPORTS FOR ADDITIVE MANUFACTURING” and filed Feb. 11, 2016;

U.S. patent application Ser. No. 15/042,024, titled “METHOD ANDCONNECTING SUPPORTS FOR ADDITIVE MANUFACTURING” and filed Feb. 11, 2016;

U.S. patent application Ser. No. 15/041,973, titled “METHODS ANDSURROUNDING SUPPORTS FOR ADDITIVE MANUFACTURING” and filed Feb. 11,2016;

U.S. patent application Ser. No. 15/042,010, titled “METHODS AND KEYWAYSUPPORTS FOR ADDITIVE MANUFACTURING” filed Feb. 11, 2016;

U.S. patent application Ser. No. 15/041,991, titled “METHODS AND LEADINGEDGE SUPPORTS FOR ADDITIVE MANUFACTURING” filed Feb. 11, 2016; and

U.S. patent application Ser. No. 15/041,980, titled “METHOD AND SUPPORTSWITH POWDER REMOVAL PORTS FOR ADDITIVE MANUFACTURING” filed Feb. 11,2016.

The disclosure of each of these application are incorporated herein intheir entirety to the extent they disclose additional support structuresthat can be used in conjunction with the support structures disclosedherein to make other objects.

Additionally, scaffolding includes supports that are built underneath anobject to provide vertical support to the object. Scaffolding may beformed of interconnected supports, for example, in a honeycomb pattern.In an aspect, scaffolding may be solid or include solid portions. Thescaffolding contacts the object at various locations providing loadbearing support for the object to be constructed above the scaffolding.The contact between the support structure and the object also preventslateral movement of the object.

Tie-down supports prevent a relatively thin flat object, or at least afirst portion (e.g. first layer) of the object from moving during thebuild process. Relatively thin objects are prone to warping or peeling.For example, heat dissipation may cause a thin object to warp as itcools. As another example, the recoater may cause lateral forces to beapplied to the object, which in some cases lifts an edge of the object.In an aspect, the tie-down supports are built beneath the object to tiethe object down to an anchor surface. For example, tie-down supports mayextend vertically from an anchor surface such as the platform to theobject. The tie-down supports are built by melting the powder at aspecific location in each layer beneath the object. The tie-downsupports connect to both the platform and the object (e.g., at an edgeof the object), preventing the object from warping or peeling. Thetie-down supports may be removed from the object in a post-processingprocedure.

A break-away support structure reduces the contact area between asupport structure and the object. For example, a break-away supportstructure may include separate portions, each separated by a space. Thespaces may reduce the total size of the break-away support structure andthe amount of powder consumed in fabricating the break-away supportstructure. Further, one or more of the portions may have a reducedcontact surface with the object. For example, a portion of the supportstructure may have a pointed contact surface that is easier to removefrom the object during post-processing. For example, the portion withthe pointed contact surface will break away from the object at thepointed contact surface. The pointed contact surface stills provides thefunctions of providing load bearing support and tying the object down toprevent warping or peeling.

Lateral support structures are used to support a vertical object. Theobject may have a relatively high height to width aspect ratio (e.g.,greater than 1). That is, the height of the object is many times largerthan its width. The lateral support structure is located to a side ofthe object. For example, the object and the lateral support structureare built in the same layers with the scan pattern in each layerincluding a portion of the object and a portion of the lateral supportstructure. The lateral support structure is separated from the object(e.g., by a portion of unmelted powder in each layer) or connected by abreak-away support structure. Accordingly, the lateral support structuremay be easily removed from the object during post-processing. In anaspect, the lateral support structure provides support against forcesapplied by the recoater when applying additional powder. Generally, theforces applied by the recoater are in the direction of movement of therecoater as it levels an additional layer of powder. Accordingly, thelateral support structure is built in the direction of movement of therecoater from the object. Moreover, the lateral support structure may bewider at the bottom than at the top. The wider bottom provides stabilityfor the lateral support structure to resist any forces generated by therecoater.

Moreover a method of fabricating an object may include consecutively,concurrently, or alternatingly, melting powder to form portions ofmultiple supports as described above. Additionally, for an objectfabricated using multiple supports, the post-processing procedures mayinclude removing each of the supports. In an aspect, a support structuremay include multiple supports of different types as described herein.The multiple supports may be connected to each other directly, or viathe object. The selection of supports for a specific object may be basedon the factors described herein (e.g., shape, aspect ratios,orientation, thermal properties, etc.)

This written description uses examples to disclose the invention,including the preferred embodiments, and also to enable any personskilled in the art to practice the invention, including making and usingany devices or systems and performing any incorporated methods. Thepatentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal language of the claims.Aspects from the various embodiments described, as well as other knownequivalents for each such aspect, can be mixed and matched by one ofordinary skill in the art to construct additional embodiments andtechniques in accordance with principles of this application.

The invention claimed is:
 1. A method for fabricating an object in apowder bed, comprising the steps of: (a) irradiating a layer of powderin the powder bed to form a fused region; (b) providing a subsequentlayer of powder over the powder bed by passing a recoater arm over thepowder bed; (c) repeating steps (a) and (b) until the object and asupport structure are formed in the powder bed, wherein the objectcomprises an upper portion defining an upper hollow region having anupper width and a lower portion defining a lower hollow region having alower width less than the upper width, the support structure comprisinga first portion and a second portion connected by a weakened portion;and (d) breaking the support structure at the weakened portion toseparate the first portion and the second portion.
 2. The method ofclaim 1, wherein the support structure has a congruent geometry to theupper hollow region and the lower hollow region.
 3. The method of claim1, wherein an upper portion of the support structure is positionedwithin the upper hollow region, the upper portion of the supportstructure defining a maximum upper width that is equivalent to the upperwidth of the upper hollow region.
 4. The method of claim 3, wherein theupper portion of the support structure has a circular disk shape.
 5. Themethod of claim 1, wherein a ratio of the upper width to an upperthickness of the first portion is between 5:1 and 50:1.
 6. The method ofclaim 1, wherein a lower portion of the support structure is positionedwithin the lower hollow region, the lower portion of the supportstructure defining a maximum lower width that is equivalent to the lowerwidth of the lower hollow region.
 7. The method of claim 6, wherein thelower portion of the support structure has a thin rectangular shape. 8.The method of claim 1, wherein a ratio of the lower width to a lowerthickness of the first portion is between 5:1 and 50:1.
 9. The method ofclaim 1, wherein a lower portion of the support structure defines amaximum lower width and an upper portion of the support structuredefines a maximum upper width, wherein half of the maximum upper widthis less than the maximum lower width.
 10. The method of claim 1, whereina portion width of each of the first portion and the second portion isless than the maximum lower width.
 11. The method of claim 1, whereinthe upper hollow region is spherical and the lower hollow region iscylindrical.
 12. The method of claim 1, wherein the upper hollow regionis enclosed with the exception of a lower opening into the lower hollowregion.
 13. The method of claim 1, wherein an outlet is defined at abottom end of the lower portion, and wherein the support structure isremovable through the outlet after breaking the support structure at theweakened portion.
 14. The method of claim 13, wherein the supportstructure is incapable of passing through the outlet prior to breakingthe support structure via the weakened portion.
 15. The method of claim1, wherein the support structure is broken into at least two parts. 16.The method of claim 1, wherein the support structure is formed as a freestanding object within the powder bed.
 17. The method of claim 1,wherein the weakened portion comprises a notch and a perforation alignedwith the notch.
 18. The method of claim 1, wherein the perforationextends from a first end to an opposing second end of the supportstructure.
 19. The method of claim 1, further comprising: (e) removingthe first portion and the second portion of the support structure fromthe object by passing the first portion and the second portion throughthe outlet of the object.